As seen in many modern technologies, such as a video recorder which uses a hard disk drive (HDD) to store data, a video game system with an internal HDD for storing game information, a television with a built-in HDD for storing video content, portable HDD's for storing pictures, videos, etc., still images, videos, music, and the like are now stored on a HDD's in many different common devices and the need for storage capacity on these HDD's is rapidly increasing. As image data are increased, surface recording density of a magnetic disk drive also needs to be increased in order to store these larger image files. Currently, in a magnetic head, technology is rapidly shifting from in-plane magnetic recording to perpendicular magnetic recording in order to achieve a high surface recording density of about 100 Gbit/in2 or more. This is because when a current surface recording method is used, thermal fluctuations of magnetization of a medium occurs when a bit length is reduced, leading to difficulties in increasing an in-plane recording density.
On the other hand, in perpendicular magnetic recording, since a medium is magnetized in a direction perpendicular to the medium, the problem of thermal fluctuation can be avoided. Moreover, since a single-pole head is used for recording and a soft under layer is provided in a medium, resulting in a small magnetic loss, recording capability is also improved. This change is also a driving force of the shift to the perpendicular recording magnetic head.
However, recording density should still be improved even for a perpendicular recording magnetic head. A recording track width may be reduced to achieve such an improvement. However, a reduction in recording track width causes a corresponding decrease in a magnetic field generated from a leading portion of a main pole to a magnetic recording medium. On the other hand, a magnetic disk drive performs recording/reproducing over a wide area from the inner circumference to the outer circumference of the magnetic recording medium. Therefore, in the inner circumference and the outer circumference of the magnetic recording medium, a magnetic head performs recording/reproducing with a skew angle of about 0° to 15° with respect to a tangent in a rotational direction of the medium.
In such recording/reproducing, if a flying surface of a main pole has a rectangular shape, an adjacent track may be erased, which is problematic since data may be stored on the adjacent track and would be lost in such a situation. To prevent this, a main pole is used for current HDD's, which has a shape such that a track width on a leading side of the main pole is narrow compared with a width on a trailing side thereof so as to meet the narrow track width. Coincidentally, the main pole has an inverted trapezoidal shape when viewed from an air bearing surface. To increase surface recoding density, a recording track width is reduced while a track portion of the main pole, which defines a recording track width, is maintained with the inverted trapezoidal shape adjusted to the skew angle. As a measure for achieving this shape, a thickness of the main pole is reduced in accordance with the reduced track width.
On the other hand, a reduction in a thickness of a main pole film causes degradation in recording performance such as a decrease in magnetic field strength and a reduction in magnetic field gradient, leading to a larger problem. In the light of these problems associated with conventional perpendicular magnetic recording heads, it would be beneficial to have a perpendicular recording magnetic head in which even if a thickness of a main pole is reduced with a corresponding reduction in a recording track width, recording performance is not degraded.